1. Field
One or more aspects of the present invention relate to a method for manufacturing a magnetic tape with a servo signal written therein, a magnetic tape with a servo signal written therein, and a servo writer.
2. Description of Related Art
In accordance with the trend toward higher recording density in the realm of information storage technologies, the data tracks of a magnetic tape designed in recent years should have extremely narrow widths. To enable the magnetic head to precisely follow such a narrow data track, a servo signal indicating a reference position of the data track is written beforehand in the magnetic tape. In a magnetic tape drive which records or retrieves data in the magnetic tape, a track-following servo control is exercised in which the servo signal recorded in advance is read out to work out an amount of deviation in position between the data track in which data is just to be recorded or retrieved and the magnetic head so that the magnetic head is regulated based on the amount of shift in position to follow the data track.
The servo signal may be written in the magnetic tape by supplying a write head of the servo writer with a recording current (pulsed signal) which causes the write head to produce a magnetic field magnetizing a portion of the magnetic tape in a predetermined direction. To be more specific, in a magnetic tape for use in longitudinal magnetic recording, as shown in FIG. 8A, a servo signal may be written by a write head WH magnetizing an unmagnetized portion of a magnetic tape MT in one direction (rightward direction in FIG. 8A) that is one of two opposite longitudinal directions of the magnetic tape MT. Alternatively, as shown in FIG. 8B, a servo signal may be written by a write head WH magnetizing a one-directionally pre-magnetized portion of a magnetic tape MT (i.e., magnetized in one of two opposite longitudinal directions of the magnetic tape MT; leftward direction in FIG. 8B), in one direction (rightward direction in FIG. 8B) opposite to the direction in which the portion is pre-magnetized. See Patent Document 1 (listed below). On the other hand, in a magnetic tape for use in perpendicular magnetic recording, as shown in FIG. 8C, a servo signal may be written by a write head WH magnetizing an unmagnetized portion of a magnetic tape MT in a direction of thickness (upward/downward direction in FIG. 8C). When the servo signal written in either way is read out, a readback signal having a waveform with a pair of peaks of opposite polarities is obtained.
Patent Document 2 (listed below) discloses that a signal having a waveform with a peak of a single polarity (this signal will hereinafter be referred to as “unipolar-pulse signal”) is used for track-following servo control exercised over the magnetic head. The use of such a unipolar-pulse signal enables increased writing density of a servo signal in the longitudinal direction of the magnetic tape, and thus results in increased speed of the track-following servo control exercised over the magnetic head.
[Patent Documents]
1. JP 2005-25820 A
2. U.S. Pat. No. 7,551,380 B2
Document 2 above, however, fails to disclose a specific method for obtaining a unipolar-pulse signal.